In intracardiac echocardiography (ICE) it may be beneficial to generate ultrasound images acquired at multiple frequencies, having the possibility of high penetration or high-resolution imaging in a single device. The objective of the presented work is to test two frequency-tunable probe prototypes in a preclinical setting: a rigid probe having a diameter of 11 mm and a new flexible and steerable 12-Fr ICE catheter. Both probes feature a forward-looking 32-element capacitive micromachined ultrasonic transducer array (aperture of 2 × 2 mm2) operated in collapse mode, which allows for frequency tuning in the 6-MHz-18-MHz range. The rigid probe prototype is tested ex vivo in a passive heart platform. Images of an aortic valve acquired in high-penetration (6 MHz), generic (12 MHz) and high-resolution (18 MHz) mode combine satisfying image quality and penetration depth between 2.5 cm and 10 cm. The ICE catheter prototype is tested in vivo using a porcine animal model. Images of an aortic valve are acquired in the 3 imaging modes with the ICE catheter placed in an ascending aorta at multiple depths. It was found that the combination of the forward-looking design and frequency-tuning capability allows visualizing intracardiac structures of various sizes at different distances relative to the catheter tip, providing both wide overviews and detailed close-ups.

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Keywords Capacitive micromachined ultrasonic transducer, Collapse mode, Frequency tunability, Intracardiac echocardiography, Medical imaging
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Journal Ultrasound in Medicine & Biology
Pekař, M, Kolen, A.F. (Alexander F.), Belt, H. (Harm), van Heesch, F. (Frank), Mihajlović, N. (Nenad), Hoefer, I.E, … van der Steen, A.F.W. (2017). Preclinical Testing of Frequency-Tunable Capacitive Micromachined Ultrasonic Transducer Probe Prototypes. Ultrasound in Medicine & Biology, 43(9), 2079–2085. doi:10.1016/j.ultrasmedbio.2017.05.005